Tumor necrosis factor-alpha stimulates the maturation of sterol regulatory element binding protein-1 in human hepatocytes through the action of neutral sphingomyelinase.
The mechanism by which genes involved in cholesterol biosynthesis and import are preferentially up-regulated in response to sterol depletion was elucidated with the cloning of sterol regulatory element binding protein-1 (SREBP-1). SREBP-1 is a transcription factor whose entry into the nucleus is gated by sterol-regulated proteolysis. We have investigated the role of tumor necrosis factor-alpha (TNF-alpha) as a mediator of SREBP-1 maturation in human hepatocytes. TNF-alpha is capable of inducing SREBP-1 maturation in a time- and dose-dependent manner that is consistent with the kinetics of TNF-alpha-mediated activation of neutral sphingomyelinase (N-SMase). Antibodies to N-SMase inhibit TNF-alpha-induced SREBP-1 maturation suggesting that N-SMase is a necessary component of this signal transduction pathway. Ceramide, a product of sphingomyelin hydrolysis, is also capable of inducing SREBP-1 maturation. The mature form of SREBP-1 generated by TNF-alpha, sphingomyelinase or ceramide treatment translocates to the nucleus and binds the sterol regulatory element. This promotes transcription of the gene upstream of the sterol regulatory element. A unique finding of our studies is that ceramide stimulated SREBP-1 maturation even in the presence of cholesterol and 25-hydroxycholesterol both of which are known suppressors of SREBP-1 maturation. Our findings indicate that ceramide-mediated maturation of SREBP-1 maturation is a novel sterol-independent mechanism by which cholesterol homeostasis may be regulated.
Lawler
J F
JF
Department of Pediatrics, Lipid Research Atherosclerosis Unit, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA.
Yin
M
M
Diehl
A M
AM
Roberts
E
E
Chatterjee
S
S
D000906:Antibodies / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001692:Biological Transport; D022762:CCAAT-Enhancer-Binding Proteins; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D010450:Endopeptidases / Q000378:metabolism; D004789:Enzyme Activation; D019084:Fluorescent Antibody Technique, Indirect; D005786:Gene Expression Regulation; D006801:Humans; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism*; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D012045:Regulatory Sequences, Nucleic Acid; D015398:Signal Transduction; D013108:Sphingomyelin Phosphodiesterase / Q000276:immunology / Q000378:metabolism* / Q000494:pharmacology; D013110:Sphingosine / Q000031:analogs & derivatives / Q000494:pharmacology; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D000906:Antibodies; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; C064769:N-acetylsphingosine; D009687:Nuclear Proteins; C497387:SREBF1 protein, human; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D013108:Sphingomyelin Phosphodiesterase; D010450:Endopeptidases; D013110:Sphingosine